On 1/30/18 3:37 PM, kdevel wrote:
On Sunday, 28 January 2018 at 19:17:49 UTC, Steven Schveighoffer wrote:
This is insane. i > 0 is used in so many places. The only saving grace
appears to be that int.min is just so uncommonly seen in the wild.
And another one that it does not happen when compiled with optimization
(-O) and also that it does not affect all the ints:
---
import std.stdio;
void foo (T) ()
{
auto i = T.min;
writefln ("%12s: %24X %12s", T.stringof, i, i > cast(T) 0);
}
void main ()
{
foo!byte;
foo!short;
foo!int;
foo!long;
}
---
byte: 80 false
short: 8000 false
int: 80000000 true
long: 8000000000000000 true
This is due to integer promotion
(https://dlang.org/spec/type.html#usual-arithmetic-conversions). Any
operation between two non-integers, first the two operands are promoted
to integers.
You can see the result here:
https://run.dlang.io/is/RAk9tE
In 32 bit mode:
byte: 80 false
short: 8000 false
int: 80000000 true
long: 8000000000000000 false
Most likely, this is due to the fact that working with longs cannot be
done natively by the CPU, so it can't use the same shifting shortcut
that causes the issue in the first place.
-Steve
